Method for fastening an assembly comprising a strain gauge

Abstract

The invention relates to a method for fastening an assembly (100) to a container intended to contain a fluid under pressure, the assembly (100) comprising a housing (1) and a strain gauge (2), the method comprising the steps of: - fastening the strain gauge (2) to the container using a second adhesive means, such as a glue, the housing (1) being free to move relative to the strain gauge (2), and fastening the housing (1) to the container using a first adhesive means so as to cover the strain gauge (2).

Description

[0001] The present invention relates to a method of fixing an assembly onto a container intended to contain a fluid under pressure, the assembly comprising a housing, an electronic acquisition card and a strain gauge, as well as a device comprising such a container and such an assembly.

[0002] A strain gauge is a sensitive element whose resistance varies when it is deformed. When the gauge is perfectly bonded to a container, such as a gas container, whose deformation under the effect of a pressurized fluid contained within the container is to be determined (such a pressurized fluid is at a pressure greater than atmospheric pressure), it deforms like the body of the container, and the deformation of the body of the container can then be determined from the deformation of the strain gauge.

[0003] Documents FR 3 016 424, US 2013 / 139897, and WO 02 / 066366 described strain gauges mounted on gas containers, such as a vehicle fuel tank or a gas cylinder. Other devices are described in documents WO 2020 / 193890 A1 and CA 3 024 810 A1. WO 2020 / 193890, for example, discloses a housing containing a strain gauge and associated electronics, the assembly being bonded to a pressurized gas cylinder.

[0004] However, bonding a strain gauge is still considered a delicate procedure today because the quality of the bond directly affects the accuracy of the strain measurement. Consequently, bonding a strain gauge must adhere to certain constraints, particularly regarding the choice of adhesive and the bonding procedure, especially when the gauge must be bonded directly to the container, such as a gas container.

[0005] Thus, in the case of a gas container, such as a gas cylinder or bottle, the strain gauge must be directly glued to the body of the container so that the deformation of the body of the container can be measured correctly.

[0006] Furthermore, it is not just a matter of fixing the strain gauge but rather the assembly including the housing, the strain gauge as well as other components, such as battery, electronic board for acquisition, processing and possible transmission of the measured data.

[0007] The problem that then arises is to be able to bond a strain gauge and fix the housing to a container, in particular a gas container, in a quick, simple and efficient way but without negatively impacting the deformation measurement carried out by the gauge, and also in a durable way (> 10 years).

[0008] From document FR 3 092 897, we know of a method for bonding an assembly comprising a housing and a strain gauge that are fixed together, the bonding being carried out in a single operation (the housing and the gauge are bonded to the bottle simultaneously). A problem exists with such a method, as the correct bonding of the strain gauge is not guaranteed.

[0009] The present invention aims to effectively overcome this drawback by providing, according to claim 1, a method for attaching an assembly to a gas container intended to hold a fluid under pressure, in particular a gas cylinder or a vehicle tank, the assembly comprising a housing, an electronic acquisition board attached to the housing, and a strain gauge, the method comprising the steps of: fix the strain gauge to the container, using a second adhesive means, such as glue, the strain gauge being fixed to the container so that it deforms with the container under the effect of the pressurized gas contained in the container, electrically connect the strain gauge and the electronic acquisition board with at least one electrical cable so that the housing remains free to move relative to the strain gauge, fix the housing to the container, using a first adhesive means, so as to cover the strain gauge and so as to provide a volume of air, between the housing and the strain gauge and / or between the strain gauge and the electronic acquisition board, the step of fixing the housing to the container being carried out after the step of fixing the strain gauge to the container.

[0010] This method allows for the correct mounting of the strain gauge, without the housing interfering with it, either during or after mounting, and during its use in measuring the deformation of the container under the effect of the pressurized gas contained within. This type of configuration also allows for greater freedom of movement between the housing (or the electronic data acquisition board) and the strain gauge, ensuring proper mounting of the strain gauge.

[0011] The invention also relates to a device, according to claim 8, comprising a gas container intended to contain a fluid under pressure, in particular a gas cylinder or a vehicle tank, and an assembly, the assembly comprising a housing, an electronic acquisition board attached to the housing and a strain gauge, the housing being glued directly to the external surface of the container by means of a first adhesive means, the strain gauge being glued directly to the external surface of the container by means of a second adhesive means comprising a methacrylate, epoxy or cyanoacrylate type glue, or mixtures thereof, the strain gauge being fixed to the container so that it deforms with the container under the effect of the pressurized gas contained in the container, the electronic acquisition board being fixed to the housing,the strain gauge being electrically connected to the electronic data acquisition board by at least one electrical cable, the electrical cable having a length greater than the distance between the electronic board and the strain gauge, the distance being that which exists when the housing is glued to the container, a free space being provided between the strain gauge and the housing and / or between the strain gauge and the electronic data acquisition board, so that neither the electronic data acquisition board nor the housing exerts a force on the strain gauge.

[0012] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given for illustrative purposes only and are in no way intended to limit the invention. [ Fig.1 ] There [ Fig.1 ] is a schematic representation of an assembly according to the invention, before being fixed to a container; [ Fig.2 ] There [ Fig.2 ] is a schematic representation of a container onto which the strain gauge of the entire [ Fig.1 ] ; ] Fig.3 ] There [ Fig.3 ] is a representation of the container of the [ Fig.2 ] on which the assembly is fixed.

[0013] With reference to the [ Fig.1 [ ] We have represented a set 100 comprising a case 1, an electronic acquisition card 3 and a strain gauge 2. The strain gauge 2 is connected to the electronic acquisition card 3 via an electrical cable 4.

[0014] With reference to the [ Fig.2 [ ] We have shown a step in a process for fixing assembly 100 to a container 10 intended to hold a fluid under pressure. In this step, the strain gauge 2 was fixed to the wall of the container 10 using a second adhesive, such as glue, the housing 1 being free to move relative to the strain gauge 2.

[0015] In the example of the [ Fig.2 ], the housing 1 is free relative to the strain gauge 2 because it is connected to the latter by the electrical cable 4, which allows it a degree of displacement relative to the strain gauge 2.

[0016] Thus, during the strain gauge 2 fixing step, the housing 1 has no impact on the quality of the fixing of the latter.

[0017] With reference to the [ Fig.3 ], we have represented the container 10 while we have carried out the step of fixing the housing 1 to the container 10, using a first adhesive means, so as to cover the strain gauge 2.

[0018] In the example of the [ Fig.3The electrical cable 4 is also covered by the housing 1. Thus, after the assembly 100 is fixed to the container 10, the housing 1 exerts no force on the strain gauge 2, which ensures correct and precise operation of the strain gauge 2. Once the housing 1 is fixed to the container 10, the strain gauge 2 is surrounded by air trapped in an internal space between the housing and the container 10. If the housing 1 is not fixed in a completely airtight manner, the internal space may become fluidic with the environment in which the container is located.

[0019] The internal space can be filled at least partially with a gas other than ambient air and the housing 1 can be fixed in a hermetic manner to the container 10.

[0020] In the example shown, container 10 is a gas cylinder. Thus, determining the deformation of the wall of gas cylinder 10 then allows, after processing the measured deformation values, the determination of the cylinder's fill level, that is, the quantity of gas it contains.

[0021] For this, the strain gauge 2 must be subjected to a deformation field identical to that exerted by the gas pressure on the external wall of the gas cylinder 10. The gauge 2 must therefore be fixed to the external wall of the gas cylinder 10.

[0022] The strain gauge 2 is also electrically connected to the electronic acquisition board 3.

[0023] The electronic acquisition card 3, such as a microprocessor-based electronic card, is mounted as a unit in the housing 1.

[0024] It includes data processing means, enabling the processing of deformation measurements taken by strain gauge 2. It also includes means for remote data transmission.

[0025] The casing 1 serves as a protective housing. It contains one (or more) electric battery(ies).

[0026] The battery provides electrical current to the strain gauge 2, the data processing means, the data transmission means, and possibly other components that require it to function.

[0027] As an example, the second adhesive is placed directly between strain gauge 2 and bottle 10. It preferably has: a glass transition temperature Tg as high as possible (> 80°C) so as not to alter the measurement by gauge 2 of the deformation of bottle 10, an elongation between 2 and 7%, i.e. close to the deformation values ​​that we want to measure, crosslinking at room temperature (typically at about 20°C) so as not to have to heat the housing 1 during the fixing procedure, a coefficient of thermal expansion (close to steel) to limit shear stresses on the gauge during variations in room temperature, high resistance to hot aging and to chemicals, and / or low viscosity to ensure homogeneous bonding in a thin layer.

[0028] To meet these constraints, methacrylate, epoxy and cyanoacrylate type adhesives, or mixtures of these adhesives, may be suitable as a second adhesive medium.

[0029] Furthermore, regarding the first adhesive means used to fix the housing 1, which includes a flattened adhesive support, such as a tape or strip, the two opposite surfaces of which are covered with one or more adhesives, advantageously a double-sided adhesive tape, it may carry the same adhesive (or adhesives) on its two opposite surfaces or, as the case may be, different adhesives.

[0030] This adhesive (or these adhesives) can also be of the methacrylate, epoxy, and cyanoacrylate type, or mixtures thereof. However, it should be emphasized that the adhesive (or adhesives) is chosen in this case to allow for rapid bonding, that is to say, (almost) instantaneous bonding upon placement of the housing 1 against the surface of the bottle 10, and preferably to ensure a seal, thereby protecting the strain gauge 2.

[0031] Advantageously, the first adhesive medium chosen is a flattened adhesive support with a thickness of approximately 0.1 to 2 mm, preferably made of a slightly deformable material (the deformability of the support allowing better conformation on non-planar surfaces), such as synthetic foam (e.g. acrylic, PE, PET, ...), typically a double-sided adhesive tape or similar.

[0032] The first adhesive method must meet at least one of the following requirements: a setting time (i.e. gluing) as short as possible (i.e. <1 minute, or even <10 sec) in order to immediately hold the assembly in place on the bottle, be watertight in order to protect strain gauge 2 against moisture, good resistance to vibration and shock, good resistance to temperatures fluctuating between -40°C and 50°C, and / or good durability (i.e. > 5 years).

[0033] As an example, the support may include a fairly thick synthetic foam, i.e. at least 0.8 mm thick, in order to accommodate a variety of bottle bend radii 10.

[0034] Advantageously, in order to obtain effective fixing of assembly 100, in particular of strain gauge 2, at least one of the following steps can be carried out: sanding the area of ​​bottle 10 where assembly 100 is to be fixed, degreasing / cleaning the area of ​​bottle 10, after sanding,

[0035] Alternatively, the first adhesive means is identical to the second adhesive means, namely for example an adhesive, in particular a methacrylate, epoxy or cyanoacrylate type adhesive, or mixtures thereof.

Claims

1. A method for fixing an assembly (100) onto a gas container (10) intended to contain a fluid under pressure, in particular a gas bottle (10) or a vehicle tank, the assembly (100) comprising a housing (1), an acquisition electronic card (3) integral with the housing (1) and a strain gauge (2), the method comprising the steps of: - fixing the strain gauge (2) to the container (10), using a second adhesive means, such as a glue, the strain gauge (2) being fixed to the container (10) such that it deforms with the container (10) under the effect of the pressurized gas that is contained in the container (10), - electrically connecting the strain gauge (2) and the acquisition electronic card (3) with at least one electric cable (4) such that the housing (1) remains free to move relative to the strain gauge (2), - fixing the housing (1) to the container (10), using a first adhesive means, so as to cover the strain gauge (2) and so as to provide a volume of air between the housing (1) and the strain gauge (2) and / or between the strain gauge (2) and the acquisition electronic card (3), the step of fixing the housing to the container being performed after the step of fixing the strain gauge to the container.

2. The method according to the preceding claim, wherein the step of fixing the housing (1) is performed such that the housing (1) and / or the electronic card (3) exerts no force on the strain gauge (2).

3. The method according to the preceding claim, wherein the second adhesive means comprises a glue of the methacrylate, epoxy or cyanoacrylate type, or mixtures thereof.

4. The method according to any one of the preceding claims, wherein the first adhesive means comprises an adhesive support comprising two opposite surfaces on which one or more glues are deposited, preferably the adhesive support comprising a double-sided adhesive tape.

5. The method according to any one of the preceding claims, wherein the first adhesive means is positioned on a lower face of the housing (1), the lower face being arranged to match the external surface of the container (10) when the housing (1) is fixed to the container (10).

6. The method according to any one of the preceding claims, wherein the second adhesive means is deposited directly on the strain gauge (2).

7. The method according to any one of the preceding claims, wherein the electric cable (4) is welded or connected by a connector to the strain gauge (2) and to the acquisition electronic card (3).

8. A device comprising a gas container (10) intended to contain a fluid under pressure, in particular a gas bottle (10) or a vehicle tank, and an assembly (100), the assembly (100) comprising a housing (1), an acquisition electronic card (3) integral with the housing (1) and a strain gauge (2), the housing (1) being glued directly to the external surface of the container (10) via a first adhesive means, the strain gauge (2) being glued directly to the external surface of the container (10) by means of a second adhesive means comprising a glue of the methacrylate, epoxy or cyanoacrylate type, or mixtures thereof, the strain gauge (2) being fixed to the container (10) such that it deforms with the container (10) under the effect of the pressurized gas that is contained in the container (10), the acquisition electronic card (3) being fixed to the housing (1), the strain gauge (2) being electrically connected to the acquisition electronic card (3) by at least one electric cable (4), the electric cable (4) having a length greater than the distance between the electronic card (3) and the strain gauge (2), the distance being that which exists when the housing is glued onto the container, a free space being provided between the strain gauge (2) and the housing (1) and / or between the strain gauge (2) and the acquisition electronic card (3), such that neither the acquisition electronic card (3) nor the housing (1) exerts a force on the strain gauge (2).

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